Gear transmission mechanisms with one main shaft and one countershaft parallel to one another have been known for some time and are in use in multiple embodiments, particularly as vehicle gearboxes. Several idly rotatable gears, so-called idler gears, are arranged on the main shaft and permanently engage with assigned rotationally fixed counter gears arranged on the countershaft. The different pairs of idler gears/counter gears correspond to the different gear ratios of the gearbox, as is generally known and therefore not explained here in detail.
The torque initiated in the transmission by the drive motor, via at least one clutch, is transmitted to the countershaft, via a countershaft gear cluster, and from there to the corresponding idler gears, via the torque-proof counter gears, arranged on the countershaft. The torque is transmitted to the main shaft and the output shaft, respectively, by coupling one of the idler gears via an assigned clutch, which subsequently actuates the drive wheels, via a differential gear.
With known gear transmission mechanisms, the countershaft is basically positioned below the main shaft with respect to the axle system of the vehicle, so that this transmission features a relatively large overall installed size below the main shaft that is generally co-axial to the transmission input shaft and the output shaft, which is often technically disadvantageous, since, apart from gearshift elements, hydraulic systems as well as an oil pan for the gearbox are mounted below the gearset arranged on the main shaft and countershaft. In such cases, a certain amount of unused free installation space remains above the gearset.
An example for a gear transmission mechanism is illustrated and described in DE 197 94 980 A1. In this transmission mechanism, the countershaft with the torque-proof counter gears arranged on it is located exactly below a main shaft with respect to the axle system of the vehicle so that most of the overall installed size of this transmission is located below the input shaft and output shaft respectively co-axial to the main shaft and little space is left for hydraulic systems and gearshift elements for the transmission.
DE 37 17 255 C2 shows a similar transmission, where the countershaft is also arranged below a main shaft. There is also an oil pan below the countershaft so that the primary overall installed size of the transmission extends far below the main shaft co-axial to the input and output shaft, respectively, and can therefore limit the ground clearance of the vehicle.
A construction design with a countershaft arranged below the main shaft can cause installation problems, particularly for double clutch transmissions since, owing to the complex activation of such a transmission, voluminous gearshift and hydraulic elements are positioned below the main shaft axis predetermined by the input and output shaft. In this case, a significant amount of excess installation space is left unused above the transmission, which is disadvantageous in modern motor vehicles because of the high packing density in the engine compartment.
An example of a gear transmission developed as a double clutch transmission, is shown in the document “Christiani—competent in the field of motor vehicles” at www.kfz-tech.de, under the caption “transmission with double clutch”, where the illustration clearly shows that because of the countershaft located at the bottom, the overall installed size is significantly displaced downward.
Against this background, the object of the invention is to create a gear transmission mechanism, where the clearance in the engine compartment of a motor vehicle can generally be used more efficiently while, at the same time, not exceeding the lower limit of the installation space.